The present invention relates to the field of stray electrical current emissions which are released by some electronic equipment, particularly where a bus interfaces with the circuitry of an electronic device. More particularly, the present invention relates to the field of suppressing unwanted electrical emissions within an upconverter at the headend of a television signal distribution network.
The use of electromagnetic signals to carry information is ubiquitous in modern society. Computers, telephones, radios, and televisions are common examples of electronic devices that use electromagnetic signals to convey data.
However, the proliferation of these devices can also create problems. For example, any of these and similar electronic devices may also emit electromagnetic radiation in addition to making use of electromagnetic signals. Additionally, stray electric currents may escape from electronic devices, particularly where a bus interfaces with circuitry. These emissions of unwanted current or electromagnetic radiation from any of these devices may be picked up by, or interfere with the operation of, some other electronic device, particularly if the two devices are in close proximity to each other.
For these reasons, efforts are made to prevent electronic devices for emitting unwanted stray current or electromagnetic radiation that might interfere with another device. In fact, government or industry standards may be established that limit the amount of such unwanted emissions that a device may emit. The standards set by CENELEC, the European Committee for Electrotechnical Standardization, are particularly stringent.
Unwanted electromagnetic emissions are measured for purposes of the CENELEC standards by placing an absorbing clamp on the device, particularly the wiring leading to and from the device. The absorbing clamp registers the amount of stray electrical current emitted by the device during operation for comparison with established standards.
Consequently, there is a need in the art for an apparatus and method of suppressing stray electrical current from being emitted by operating electronic devices. Particularly, there is a need in the art for an apparatus and method of suppressing the emission of unwanted electric current from an upconverter at the headend of a television signal distribution network, particularly where the control signal bus interfaces with the upconverter circuitry.
It is an object of the present invention to meet the above-described needs and others. Specifically, it is an object of the present invention to provide a method and apparatus for suppressing unwanted electrical current emissions from electronic devices, particularly in an upconverter for television signal distribution from a headend signal station.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The objects and advantages of the invention may be achieved through the means recited in the attached claims.
To achieve these stated and other objects, the present invention may be embodied and described as an electronic device including a device circuit with suppressed emissions of electrical current and electromagnetic radiation. In an important application of the present invention, the device circuit may be an upconverter for converting an IF television signal to a VHF or UHF television signal.
In a particular embodiment, a device according to the present invention includes a device circuit disposed within the device; a bus interface connected to input and output busses for providing data to and from the device, and input and output lines connected between the bus interface and the device circuitry. The bus interface is spaced apart from the device circuit by a distance adequate to suppress electromagnetic emissions caused by the interaction of the bus interface and the device circuitry. The present invention may also include a filtering device for suppressing electromagnetic emissions along each of the input and output lines between the bus interface and the device circuit.
For additional suppression of electromagnetic emissions, the bus interface may be disposed on an exterior surface of a housing for the device circuit. Preferably, the bus interface is disposed in a separate interface housing disposed on the exterior surface of the device housing, where the interface housing is more heavily shielded against electromagnetic emissions than the device housing.
The improved bus interface of the present invention may include an input connector connected to the input bus; an output connector connected to the output bus; and an internal connector connected to the input and output lines. The input and output connectors are both multi-pin connectors in which five pins of the input connector are connected, respectively, five pins of the output connector.
Two pairs of the mutually connected pins of the input and output connectors are then connected through an integrated circuit to the internal connector. While another pair of the mutually connected pins of the input and output connectors is connected through a circuit comprising two transistors to the internal connector. The circuit with two transistors includes (1) a first transistor having a grounded emitter, a collector connected to a voltage source and a base connected to the internal connector; and (2) a second transistor having an emitter connected to the internal connector, a collector connected to the collector of the first transistor and a base connected to the voltage source. The mutually connected collectors of the first and second transistors are also connected to a pin of the input connector.
The present invention also encompasses a method of suppressing emissions of electrical current or electromagnetic radiation in an electronic device that includes a device circuit. The method includes spacing a bus interface connected to input and output busses apart from the device circuit by a distance sufficient to suppress the emissions of stray current or electromagnetic radiation caused by interaction of the device circuit and the interface; and connecting input and output lines between the bus interface and the device circuitry. The method of the present invention may also include filtering unwanted electromagnetic signals from each of the input and output lines to further suppress electromagnetic emissions.
With regard to the placement of the bus interface, the method may include mounting the bus interface on an exterior surface of a housing for the device circuit. This may include mounting the bus interface in an interface housing disposed on the exterior surface of the device housing, in which the interface housing is more heavily shielded against electromagnetic emissions than the device housing.
Again, an important application of the method of the present invention is upconverting an IF television signal to a VHF or UHF television signal with the device circuit, the IF television signal being provided over the input bus and the input line through the bus interface and the VHF or UHF television signal being provided over the output line to the output bus through the bus interface.